Perpendicular magnetic recording medium and magnetic recording apparatus

• US 7,901,801 B2
• Filed: 07/02/2008
• Issued: 03/08/2011
• Est. Priority Date: 07/04/2007
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Oikawa, Soichi, Maeda, Tomoyuki
• Primary Examiner(s): Ruthkosky; Mark
• Assistant Examiner(s): Harris; Gary D
• Application Number:
  US12/166,592
• Publication Number:
  US 20090011281A1
• Time in Patent Office: 979 Days
• Field of Search: None
• US Class Current: 428/827
• CPC Class Codes: G11B 5/672 having different compositions in a plurality of magnetic layers, e.g. layer compositions having differing elemental components or differing proportions of elements
• CPC Class Codes: G11B 5/676 having magnetic layers separated by a nonmagnetic layer, e.g. antiferromagnetic layer, Cu layer or coupling layer
• CPC Class Codes: G11B 5/7379 Seed layer, e.g. at least one non-magnetic layer is specifically adapted as a seed or seeding layer
• CPC Class Codes: Y10T 428/115 Magnetic layer composition

Abstract

According to one embodiment, a perpendicular magnetic recording medium includes a substrate, and a first magnetic layer and a second magnetic layer formed on the substrate, in which supposing that, for the first and second magnetic layers, respectively, uniaxial magnetic anisotropy constants are Ku₁ and Ku₂, saturation magnetizations are Ms₁ and Ms₂, anisotropic magnetic fields are Hk₁ and Hk₂ and the thicknesses are t₁ and t₂, then following conditions are satisfied that Ku₁ and Ku₂ are 3×10⁶ erg/cc or more, Ms₁ is smaller than Ms₂, Hk₁ is larger than Hk₂ and t₁ is larger than t₂.

Claims

1. A perpendicular magnetic recording medium comprising:

a substrate; and

a first magnetic layer and a second magnetic layer formed on the substrate,

wherein, for the first and second magnetic layers, respectively, uniaxial magnetic anisotropy constants are Ku₁ and Ku₂, saturation magnetizations are Ms₁ and Ms₂, anisotropic magnetic fields are M₁ and Hk₂, and the thicknesses are t₁ and t₂, then following conditions are satisfied;

Ku₁ and Ku₂ are 3×

10⁶ erg/cc or more;

Ms₁ is smaller than Ms₂;

Hk₁ is larger than Hk₂; and

t₁ is larger than t₂.

2. The perpendicular magnetic recording medium according to claim 1, wherein the first magnetic layer includes crystal grains comprising Co, Pt and Cr and amorphous grain boundaries, and the second magnetic layer includes Co but no Cr.

3. The perpendicular magnetic recording medium according to claim 1, wherein the second magnetic layer includes only Co or contains Co and at least one of Pt and Pd.

4. The perpendicular magnetic recording medium according to claim 1, wherein the second magnetic layer includes amorphous grain boundaries comprising at least one selected from the group consisting of Si, Cr and Ti in a larger proportion than in crystal grains.

5. The perpendicular magnetic recording medium according to claim 1, further comprising a nonmagnetic intermediate layer between the first magnetic layer and second magnetic layer, the first magnetic layer and second magnetic layer being ferromagnetically coupled.

6. The perpendicular magnetic recording medium according to claim 5, wherein the nonmagnetic intermediate layer includes at least one of Pt and Pd.

7. The perpendicular magnetic recording medium according to claim 1, wherein a perpendicular squareness is approximately 1.

8. The perpendicular magnetic recording medium according to claim 1, wherein an inclination α

of a perpendicular magnetization curve at coercivity Hc is 1 or more.

9. The perpendicular magnetic recording medium according to claim 1, further comprising a soft magnetic underlayer comprising Co and Zr between the substrate and the first magnetic layer.

10. The perpendicular magnetic recording medium according to claim 9, further comprising a nonmagnetic underlayer comprising Ru between the soft magnetic underlayer and the first magnetic layer.

11. The perpendicular magnetic recording medium according to claim 10, further comprising a seed layer comprising at least one selected from the group consisting of Pd, Pt, Ni, Ta and Ti between the soft magnetic underlayer and the nonmagnetic underlayer.

12. A magnetic recording apparatus comprising:

the perpendicular magnetic recording medium according to claim 1; and

a single-pole type magnetic recording head.